%0 Journal Article
%A Quijano López, María Luisa
%A Castro Jiménez, Jose Manuel
%A Pancost, Richard D.
%A Gea Guillén, Ginés Alfonso
%A Najarro, María
%A Aguado Merlo, Roque
%A Rosales, Idoia
%A Martín Chivelet, Javier
%T Organic geochemistry, stable isotopes, and facies analysis of the Early AptianOAE—New records from Spain (Western Tethys)
%D 2012
%@ 0031-0182
%U https://hdl.handle.net/20.500.14352/43670
%X The Early Aptian Oceanic Anoxic Event (OAE1a) is a time interval characterized by increased organic carbonaccumulation in marine sediments, notable sedimentary and biotic changes, and abrupt carbon-isotopeexcursions indicative of significant major palaeoenvironmental changes linked to a perturbation in the globalcarbon cycle. Here we present the study of four sections recording the OAE1a (Early Aptian) in Spain, whichare located in two broad basins respectively located in the South and the North of Iberia: the Southern IberianPalaeomargin (Carbonero, La Frontera and Cau sections) and the Basque–Cantabrian Basin (Puentenansasection), which represent depositional settings ranging from shallow marine (distal ramp -Cau- and drownedplatform -Puentenansa-) to pelagic environments (Carbonero, La Frontera). Biomarker compositions,C-isotope profiles, biostratigraphic data and facies analysis from the four sections are correlated and integrated.The C-isotope curves all present a clear negative excursion followed by a positive shift. The integration ofthe C-isotope curves with the biostratigraphic data has been used to correlate the studied sections and to tentativelyidentify the eight segments formerly proposed from the Alpine domain, and subsequently identifiedin sections worldwide. Four main groups of compounds are present in all sections: n-alkanes, isoprenoids,hopanes and steranes. n-Alkanes and acyclic isoprenoids (pristane and phytane) are dominant in most samples.The hopanes are represented by a range of C27 to C35 components,with the specific isomers varying amongst thesections due to differences in thermal maturity. Steranes occur as a range of C27, C28 and C29 isomers, whereasdiasteranes only occur in the most thermally mature section (Carbonero). Other compounds of interest includegammacerane and dinosterane. Differences in thermal maturity appear to be the first order control on differentbiomarker assemblages amongst the studied sections. The Carbonero section is thermally mature, whereas thenearby La Frontera and Cau sections are immature. Puentenansa has intermediate values. Organic matter is derivedfrom a range of terrestrial, marine and bacterial sources. The dominance of the C29 sterane isomers in allsections suggests a strong contribution from higher plants. The presence of gammacerane indicates water columnstratification, and high C29/C30 hopane ratios suggest anoxia at the water/sediment interface, respectively.Sedimentologic analysis also suggests anoxic conditions during sedimentation, but evidence for strong and persistentwater column anoxia is equivocal. The correlation of the sections reveals that sedimentation oforganic-rich facies started earlier in pelagic and later in the shallow marine settings, which can be related toan expansion of the favorable conditions for organic matter accumulation and preservation from deep marinewaters to shallower platform environments during the development of OAE1a.
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